A no mode hopping and narrow linewidth external-cavity wavelength-swept laser (EC-WSL) based on a traditional Littman-Metcalf structure is proposed and experimentally demonstrated. The wavelength scanning output range of the proposed laser without mode hopping is from 1520.82 nm to 1579.95 nm (namely, 59.13 nm). The narrow spectral linewidth less than 100 kHz is simultaneously realized. Meanwhile, the output power of the presented laser exceeding 14.8 dBm over the entire wavelength scanning range is obtained. In view of the good tuning characteristics, we achieved now, the proposed EC-WSL may be used in practical engineering fields such as gas detection.
We propose and demonstrate experimentally a direct-detection single-end Brillouin temperature sensing system based on single-photon detector to evaluate the ambient temperature along the sensing link, which is an excellent candidate for the demodulation of frequency shift from Brillouin gain spectrum in traditional Brillouin configurations. In the proposed method, the ratio of the Rayleigh backscattering component and the Brillouin anti-Stokes component is used to demodulate the temperature information along the measured optical fiber link. Proof-of-concept experiment proves that a spatial resolution of 1.2m over 4.2km sensing range with a 1.24°C temperature error can be obtained. Additionally, the proposed direct-detection Brillouin sensor maintains large dynamic range, which boosts its practicability.
We propose and experimentally validate a distributed refractive index (RI) sensor obtained by simply bending a piece of standard single mode fiber (SMF) to a radius of curvature in several millimeters with intact buffer coating. The RI of the external medium surrounding the U-bent optical fibers is measured by the wavelength shifts of the local Rayleigh backscattered spectra when the RI ranges from 1.3330 to 1.3773. To demonstrate the ability of distributed RI sensing based on the proposed method, this presented sensing element is employed to measure multipoint RI variations at the same time. The sensitivities are about 19.61nm/RIU (RI units), 27.59nm/RIU and 39.08nm/RIU in the proposed structure, respectively.
We developed a distributed refractive index (RI) sensor based on high performance optical frequency-domain reflectometry (OFDR) by simply bending a piece of standard single mode fiber (SMF) in a U shape. In the U-bent region, cladding modes are excited, which can reach to the boundary of the SMF to sense external RI variation. The cladding modes are then coupled back to the core mode and interfere with the fundamental mode. Thus, the fundamental mode can carry the varied RI information, and distributed index sensing is achieved by measuring the wavelength shifts of the local Rayleigh backscattered spectra. Thanks to the high signal SNR of OFDR, that compensating the bending induced loss, the proposed sensor can be bent in a small bending radius so that a high sensitivity of RI could be achieved. In the experiment, index sensitivity of 39.08 nm/RIU is achieved by imposing a bending radius of 4 mm, when the RI ranges from 1.3330 to 1.3773. Additionally, the proposed sensor maintains buffer coating intact, which boosts its practicability and application flexibility.
Utilizing the single-photon detector, a direct-detection single-end Brillouin optical-fiber sensor is proposed and experimentally demonstrated for distributed temperature information measurement, which is an excellent candidate for the demodulation of frequency shift from Brillouin gain spectrum in conventional Brillouin schemes with coherent detection and frequency sweep. In our scheme, the ratio of the backscattered Rayleigh component and the Brillouin anti- Stokes signal is used to evaluate the ambient temperature along the fiber under test. Proof-of-concept experiments demonstrate 20dB dynamic range over 34km sensing fiber with a 0.96°C temperature error. In view of the good characteristics we achieved now, the photon-counting distributed Brillouin temperature sensor may be used in practical engineering fields such as smart grid.
A unique multi-parameter sensor for distributed measurement of temperature and strain based on spontaneous Brillouin scattering in communication optical fiber is proposed, which is an excellent candidate for the crosstalk effects in conventional Brillouin sensing network. In experimental section, the discrimination of strain and temperature is successfully demonstrated by analyzing the unequal sensing coefficients of the Brillouin frequency shifts generated by different acoustic modes. The Brillouin frequency shifts of first two three peaks are successfully measured to discriminate the strain and temperature with an accuracy 19.48με and 0.93°C in 10km sensing range. The proposed distributed Brillouin optical fiber sensor allows simultaneously temperature and strain measurement, thus opening a door for practical application such as smart grid.
Lidar has been widely used in both military and civil applications. Its received optical signal undergoes considerable loss and disturbance from background noise, which limits its performance especially in bad weather or air conditions. A high-gain and frequency-selective amplifier for weak optical signal based on stimulated Brillouin scattering in single mode fiber is proposed, which is an excellent candidate for the signal enhancement in lidar system. The characteristics of the amplifier were studied numerically and experimentally. In experiment, a 430-nW (peak power) pulsed signal was amplified by 70 dB with a signal-noise ratio of 14 dB, which was in good agreement with theoretical result.
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